Duplex Configuration
A duplex communication system is a point-to-point system supporting communications between two parties or devices in both directions.
A half-duplex (HDX) system supports communications between two parties or devices in both directions, but in only one direction at a time (not simultaneously). A full-duplex (FDX), or sometimes double-duplex system, supports communications between two parties or devices in both directions at the same time (simultaneously).
Time-division duplexing (TDD) is the application of time-division multiplexing to separate outward and return signals but on the same carrier frequency, i.e., operating over a half-duplex communication link.
Frequency-division duplexing (FDD) means that the transmitter and receiver operate at different carrier frequencies, typically separated by a frequency offset.
The Long Term Evolution (LTE) standard provides for both FDD and TDD operation modes. Additionally, half duplex operation is also specified, which is essentially an FDD operation mode but with transmission and reception not occurring simultaneously, similar to TDD schemes. Half-duplex mode may have advantages with some frequency arrangements where a duplex filter may not be reasonable, e.g., resulting in relatively high cost and/or relatively high power consumption. Since a carrier frequency number (EARFCN or EUTRA Absolute Radio Frequency Channel Number) is unique, by knowing it, it is possible to determine the frequency band, which corresponds to either FDD or TDD. However, it may be more difficult to detect the difference between full-duplex FDD and half-duplex FDD (HD-FDD) without explicit information since a same FDD band can be used as full FDD or HD-FDD.
In 3GPP, two radio frame structure types are currently supported: Type 1 (applicable to FDD) and Type 2 (applicable to TDD).
Transmissions in multiple cells can be aggregated where up to four secondary cells can be used in addition to the primary cell. In case of multi-cell aggregation, the UE (also referred to as a user equipment node and/or a wireless device/terminal) currently assumes the same frame structure is used in all the serving (primary and secondary) cells.
FDD
Frame structure type 1 is applicable to both full duplex and half duplex FDD, and frame structure type 1 may be provided as illustrated in FIG. 1.
For FDD, 10 subframes are available for downlink transmission and 10 subframes are available for uplink transmissions in each 10 ms interval. Uplink (UL) and downlink (DL) transmissions are separated in the frequency domain in that the UL and DL transmissions take place over different carrier frequencies. In half-duplex FDD operation, the UE cannot transmit and receive at the same time while there are no such restrictions in full-duplex FDD. There is no need for guard periods for full-duplex FDD. For half-duplex FDD operation, a guard period is created by the UE by not receiving at least the last part of a downlink subframe immediately preceding an uplink subframe from the same UE.
TDD
The frame structure type 2, applicable for TDD, is as illustrated in FIG. 2.
UL/DL TDD Configurations
The table of FIG. 3 illustrates UL/DL TDD configurations defined so far in 3GPP (3rd Generation Partnership Project), where, for each subframe in a radio frame: “D” denotes the subframe is reserved for downlink transmissions; “U” denotes the subframe is reserved for uplink transmissions; and “S” denotes a special subframe with the three fields DwPTS (the downlink part of the special subframe for TDD operations), GP (TDD guard period), and UpPTS (the uplink part of the special subframe for TDD operations). Choosing a specific UL/DL configuration may be determined, e.g., based on traffic demand in DL and/or UL and/or network capacity in DL and/or UL.
Subframes 0 and 5 and DwPTS are always reserved for downlink transmission. UpPTS and the subframe immediately following the special subframe are always reserved for uplink transmission.
The length of DwPTS and UpPTS depends on the combination of DL and UL cyclic prefix lengths and on the special subframe configuration (10 pre-defined special subframe configurations are defined in TS 36.211). Typically, DwPTS is longer than UpPTS.
In case multiple cells are aggregated, the UE may assume that the guard period of the special subframe in the different cells have an overlap of at least 1456Ts.
Existing Capabilities Related to Duplex Configuration Support
Supported RF (Radio Frequency) Band(s)
Radio network nodes and UEs typically may not support all RF bands (aka operating frequency bands), but a subset of the RF bands. Currently, the RF bands supported by the UE may be signaled to the serving eNB (also referred to as an eNodeB and/or a base station) or positioning node (E-SMLC or Evolved Serving Mobile Location Center). Base stations typically declare supported RF bands; although some radio network nodes, e.g., LMUs (Location Measurement Units), may signal the RF bands they support to another node (e.g., a positioning node). An RF band and a duplex mode may be indirectly indicated by the carrier frequency number (EARFCN), which is unique, and by knowing the carrier frequency number, the frequency band it belongs to may be determined. The RF band, in turn, is either FDD or TDD, though it may not be possible to tell from EARFCN whether it is FDD or HD-FDD.
Half-Duplex FDD (HD-FDD) Capability
The HD-FDD capability for UEs has been discussed, e.g., for low-cost devices. From the network side, HD-FDD may be supported by means of scheduling, which would also allow the radio network nodes to support both non HD-FDD and normal FDD UEs.
DL (DownLink) CA (Carrier Aggregation) with different UL/DL TDD configurations.
In Rel-11, this capability becomes mandatory for all Rel-11 UEs supporting TDD and inter-band CA (DL only).
Network Deployments Using Non-Full Duplex Operation Modes
Non-full duplex operation modes, e.g., HD-FDD or TDD, may have some advantages such as lower device complexity (e.g., no need for duplex filter), channel reciprocity (the channel estimates on UL may very well reflect the channel in DL, especially for slow-varying channels), and possibility to better adapt spectrum utilization to unbalanced DL and UL traffic. A typical disadvantage, however, may be the generated co-channel interference and even inter-channel/inter-band interference, which may require, for example, additional rather large guard bands to reduce unwanted emissions to other systems.
Examples of deployments using non-full duplex operation modes are discussed below. Proposed deployments may also provide means to enable and/or improve performance in such deployments, without precluding also other deployments.
Single-Carrier and Multi-Carrier Deployments
Non-full duplex operation may be used in single-carrier or multi-carrier deployments, with the same or different duplex configurations or even different duplex modes (e.g., FDD and TDD) in different carriers, which may be determined by the spectrum availability in the area, wireless communications system purpose, services, and traffic needs.
Dynamic TDD
Typically dynamic TDD operation refers to changing TDD configurations over a time period on a carrier of a single-carrier or multi-carrier deployment, but such operation may also be implemented over multiple carriers.
Different UL/DL Configurations
It has been agreed in 3GPP, that all UEs should support different UL/DL configurations on different bands. This applies for non-CA operation, but also for inter-band CA (currently the UEs support DL CA for inter-band, but UL CA for inter-band is likely to be supported in a later release too). As mentioned earlier, a specific UL/DL configuration may be decided based on different factors, e.g., traffic demand in DL and/or UL.
In the current standard, different UL/DL configurations in different cells are assumed to be statically configured. Different UL/DL configurations may be configured statically or dynamically in different bands, only in presence of a sufficient inter-band separation. Indeed, the possibility of having different UL/DL configurations can also give more flexibility for dynamic TDD and hence can be combined with the latter, which, however, would make interference coordination in the network more challenging in case of insufficient separation between bands or especially on the same carrier.
Small Cells and Heterogeneous Deployments
The interest in deploying low-power nodes (such as pico base stations, home eNodeBs, relays, remote radio heads, etc.) for enhancing the macro network performance in terms of the network coverage, capacity and service experience of individual users has been constantly increasing over the last few years. At the same time, a need has been recognized for enhanced interference management techniques to address arising interference issues caused, for example, by significant transmit power variation among different cells and cell association techniques developed earlier for more uniform networks.
In 3GPP, heterogeneous network deployments have been defined as deployments where low-power nodes of different transmit powers are placed throughout a macro-cell layout, implying also non-uniform traffic distribution. Such deployments, for example, may be effective for capacity extension in certain areas, so-called traffic hotspots, i.e., small geographical areas with a higher user density and/or higher traffic intensity where installation of pico nodes can be considered to enhance performance. Heterogeneous deployments may also be viewed as a way of densifying networks to adapt to the traffic needs and the environment. However, heterogeneous deployments may also bring challenges for which the network has to be prepared to ensure efficient network operation and superior user experience. Some challenges are related to increased interference in the attempt to increase small cells associated with low-power nodes, also known as cell range expansion. Other challenges are related to potentially high interference in uplink due to a mix of large and small cells.
According to 3GPP, heterogeneous deployments consist of deployments where low power nodes are placed throughout a macro-cell layout. The interference characteristics in a heterogeneous deployment can be significantly different than in a homogeneous deployment, in downlink or uplink or both. Examples of such interference in heterogeneous deployments are illustrated in FIG. 4, where in case (a), a macro user UE-a with no access to the Closed Subscriber Group (CSG) cell may experience interference from the HeNodeB low power node LPN-a, in case (b) a macro user UE-B may generate severe interference for the HeNodeB low power node LPN-b, in case (c) a CSG user UE-C may receive interference from another CSG HeNodeB low power node LPN-c, and in case (d) a UE UD-d may be served by a pico cell LPN-d in the expended cell range area ECR. In general, a heterogeneous deployment does not necessarily involve CSG cells.
One of the baseline deployments for LTE Rel-12 is a deployment with small cells deployed on a separate carrier. It is also expected that traffic patterns may be quite different in small cells, which may justify different duplex modes and even different duplex configurations (if the same mode is used) on the carrier with macro cells and the carrier with small cells.
Positioning Architecture in LTE
As shown in FIG. 5, three significant network elements in an LTE (Long Term Evolution) positioning architecture include the LCS (Location Service) Client, the LCS target, and the LCS Server. The LCS Server is a physical or logical entity managing positioning for a LCS target device by collecting measurements and other location information, assisting the wireless device/terminal (UE) in measurements when necessary, and estimating the LCS target location. A LCS Client is a software and/or hardware entity that interacts with a LCS Server for the purpose of obtaining location information for one or more LCS targets, i.e., the entities being positioned. LCS Clients may also reside in the LCS targets themselves. An LCS Client sends a request to LCS Server to obtain location information, and the LCS Server processes and serves the received requests and sends the positioning result and optionally a velocity estimate to the LCS Client. A positioning request can be originated from the wireless device/terminal or a network node or external client.
Position calculation can be conducted, for example, by a positioning server (e.g., E-SMLC or SLP or Secure User Plane Location Location Location Platform in LTE) or UE. The former approach corresponds to the UE-assisted positioning mode, while the latter corresponds to the UE-based positioning mode.
Two positioning protocols operating via the radio network exist in LTE, LPP (LTE Positioning Protocol) and LPPa. The LPP is a point-to-point protocol between a LCS Server and a LCS target device, used to position the UE (aka target device). LPP can be used both in the user and control plane, and multiple LPP procedures are allowed in series and/or in parallel thereby reducing latency. LPPa is a protocol between eNodeB and LCS Server specified only for control-plane positioning procedures, although it still can assist user-plane positioning by querying eNodeBs for information and eNodeB measurements. SUPL (Secure User Plane Location) protocol is used as a transport for LPP in the user plane. LPP has also a possibility to convey LPP extension messages inside LPP messages, e.g., currently OMA (Open Mobile Alliance) LPP extensions are being specified (LPPe) to allow, for example, for operator-specific assistance data or assistance data that cannot be provided with LPP or to support other position reporting formats or new positioning methods.
A high-level architecture, as it is currently standardized in LTE, is illustrated in FIG. 6, where the LCS target is a wireless device/terminal UE, and the LCS Server is an E-SMLC or an SLP. In FIG. 6, the control plane positioning protocols (e.g., LPP, LPPa, and LCS-AP) are shown terminating (at one end) at E-SMLC, and the user plane positioning protocol (e.g., SUPL/LPP) is shown terminating (at one end) at SLP. The SLP may comprise two components/elements, SPC (SUPL Location Center) and SLC (SUPL Location Platform), which may also reside in different nodes. In an example embodiment, SPC has a proprietary interface with E-SMLC, and L1p interface with SLC, and the SLC part of SLP communicates with P-GW (PDN-Gateway or Packet Data Network Gateway) and External LCS Client.
Additional positioning architecture elements may also be deployed to further enhance performance of specific positioning methods. For example, deploying radio beacons may be a cost-efficient solution which may significantly improve positioning performance indoors and also outdoors by allowing more accurate positioning, for example, with proximity location techniques.
For UL positioning (e.g., UTDOA or Uplink-Time Difference of Arrival), location measurement units (LMUs) may also be included in the positioning architecture (see FIG. 5). The LMUs may be, for example, standalone, integrated into eNodeB, or co-sited with an eNodeB. In LTE, UTDOA measurements, UL RTOA (Relative Time of Arrival), are performed on Sounding Reference Signals (SRS). To detect an SRS signal, an LMU needs a number of SRS parameters to generate the SRS sequence which is to be correlated to receive signals. SRS parameters would have to be provided in the assistance data transmitted by positioning node to LMU. This assistance data would be provided via LMUp. However, these parameters are generally not known to the positioning node, which may then need to obtain this information from an eNodeB configuring the SRS to be transmitted by the UE and measured by LMU. This information may have to be provided using LPPa or a similar protocol.
In networks where a non-full duplex mode (e.g., TDD or HD-FDD) is used, performing measurements with different UL/DL (UpLink/DownLink) subframe configurations in such networks may be difficult.
Approaches described in this Background section could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise expressly stated herein, the approaches described in this Background section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.